A digital copying machine, which is an example commercialized image forming apparatus, makes a copy of an original image in the following manner. Firstly, an image reading section reads an original image, secondly, an image processing section processes the read image in a specified manner, and finally, a recording section outputs data of the processed image (processed image data) on a sheet as a hard copy. Where a single digital copying machine is used, only the image processing functions pre-installed therein are available to form an image on a sheet.
On the other hand, an idea of forming a network by interconnecting a plurality of image recording apparatuses or the like has been proposed recently. More specifically, a digital copying machine or the like is connected to a plurality of image input apparatuses through a communication line, so that the digital copying machine can output the image data transmitted from any of the image input apparatuses onto a sheet as a hard copy.
For example, Japanese Laid-Open Patent Application No. 116834/1978 (Tokukaisho No. 53-116834) discloses an arrangement to interconnect a plurality of image reading apparatuses and a plurality of image recording apparatuses through a single control section, so that each image reading apparatus can communicate with any of the image recording apparatuses.
This arrangement enables each image recording apparatus to output a hard copy of original image data read by and sent from any of the image reading apparatuses through the control section. Thus, the idle time of the image recording apparatuses while replacing the original documents at the image reading apparatus can be reduced. Also, the output time can be cut by using a desired number of image recording apparatuses.
Also, Japanese Laid-open Patent Application No. 198958/1986 (Tokukaishou No. 61-198958) (Japanese Examined Patent Publication No. 36592/1995 (Tokukouhei No. 7-36592) or U.S. Pat. No. 4,797,706) discloses an image forming system including a plurality of copying machines interconnected through a single control apparatus, and each copying machine is furnished with an image read section and an image record section.
In this image forming system, image data subject to recording are distributed to more than one copying machine furnished with a specific image copying mode the user wishes to use, and all the copying machines that received the image data carry out the copying job in parallel. In other words, the image forming apparatuses furnished with the specific copying mode are selected to share the copying (image forming) job.
However, the above conventional image forming systems have a problem.
That is, each image processing function of the digital copying machine depends on software programs, which have been developed at an increasing pace. Thus, the image processing function is upgraded in a short period and new models with additional functions have been steadily commercialized. Therefore, the state-of-the-art digital copying machine with desired image processing functions becomes an outdated, relatively low-level model as soon as the user purchases it.
Because the user can neither upgrade the functions pre-installed in his digital copying machine nor simply add new functions, if he wants higher level or new functions, he has to purchase a new model. This is an economic burden to the user and a manufacturers' problem conflicting with their efforts in trying to always meet users' demands.
Once a state-of-the-art digital copying machine furnished with new functions has become available, it lures the users who wish to upgrade an image output further to their satisfaction.
To solve the above problem, the inventors of the present invention have proposed a following image forming system. That is, an original image read by any of the copying machines is processed by one of the other copying machines furnished with a specific image processing function. Then, the processed image data are returned to the image-reading copying machine from the data-processing copying machine, so that the image-reading copying machine can print out the returned processed image data. According to this arrangement, even if the user uses an old digital copying machine which is not furnished with an image processing function he wishes to use, the job can be finished also using a new copying machine within the system furnished with that specific image processing function. Thus, if at least one digital copying machine within the system is furnished with new functions, not all the old digital copying machines need to be replaced with new ones, thereby making it possible to fully utilize the old digital copying machines.
However, this system causes a following problem. That is, while the image-reading copying machine is having access to the data-processing copying machine to output hard copies using the new function of the data-processing copying machine, the use of the data-processing copying machine is restricted to the image-reading copying machine alone, and the access to the data-processing copying machine from any other copying machine within the system is blocked. If there occurs a trouble in the image-reading copying machine under these conditions, not only the access to the data-processing copying machine remains blocked, but also the hard copies can not be outputted from the data-processing copying machine either until the trouble is removed. Thus, the image processing using this system is not as efficient as it had been expected.
In addition, if the copying machine that reads an original image has a small storage capacity, the job is carried out in the following manner. That is, original image data read by the copying machine with a small storage capacity are temporarily stored in the storage section of another copying machine within the system and returned to the image-reading copying machine when printed out.
However, once the image-reading copying machine issues a store request to any of the other copying machines to store the image data on its behalf, the request-receiver copying machine withholds the image data until it receives a return request from the image-reading copying machine even if the stored image data become useless for the image-reading copying machine for some reason. Thus, the useless image data are left in the memory of the request-receiver copying machine and occupy the same over a long period, which becomes a capacitive burden to the request-receiver copying machine during its own copying operation.